The present invention relates to an auto ranging apparatus for use with photographic cameras or the like for determining the distance-to-subject range and, more particularly, to an auto ranging system that utilizes diffracted radiation either emitted by or reflected from the subject of principal interest for accurately determining the distance-to-subject range.
Motion picture and still picture cameras are typically focused by manual adjustment of the camera lens while viewing a focus indicator such as the split/image screen on the so-called range-finder cameras and the focusing screen provided in single-lens-reflex camera. Automatic or auto ranging focusing systems have been developed which permit the camera to auto range, that is, determine the distance-to-subject range without the intervention of a camera operator. These automatic systems have typically utilized radiation that is either emitted by or reflected from the subject of principal interest. The radiation, which may be in the visible or infra-red light range, is typically focused on a radiation responsive sensor or sensors with the relative position of the focused image on a sensor or the positional coincidence between the focused images on plural sensors used as a basis for determining the distance-to-subject range. As a practical matter, the radiation responsive sensors are typically of small physical size (e.g., 5 mm. on a side). Since the distance-to-subject range is dependent upon the position that the focused energy from the subject falls on the comparatively small sensor(s), it is important that the focusing be relatively sharp to provide acceptable accuracy in the range determination. While prior systems have been developed which provide adequate ranging information, the resolution of these prior systems has been limited by the practical need for physically compact ranging sensors.